Embryo transfer is the last step in the in vitro fertilization process. A proper transfer is critical to the success of the procedure. This is a delicate process and requires placement of the embryos in the most appropriate location of the endometrial cavity while minimizing trauma and unnecessary manipulation of the uterine milieu.
2D Ultrasound is currently considered the most effective technique for guiding the embryo transfer. Briefly, the physician inserts an embryo-loaded catheter through the cervical opening up into the middle of the uterus under ultrasound guidance. Continuous visibility of the catheter is frequently difficult as the catheter tip can get out of plane with the 2D ultrasound. Extensive research has determined that the optimal location for embryo placement is in the middle of the endometrial cavity—halfway from the internal cervix surface to the uterine fundus. The catheter should be positioned between the top and bottom layers of the endometrium with care taken not to dissect the endometrial surface, as sub-endometrial transfers result in lower success rates. Although considered to be the best guidance method, visualization of the critical structures can be difficult.
Recently, 3D/4D ultrasound has been introduced and has begun to be used in a number of sites. It provides improved visualization of the underlying anatomy for planning. However, image quality is still less than ideal for these procedures and is sonographer-dependent.